With continuous development of the science and technologies, the electromagnetic wave technologies have found wide application in various aspects of people's life gradually. An important property of electromagnetic waves is that they can propagate in any media or even in a vacuum. During propagation of an electromagnetic wave from a transmitting end to a receiving end, the energy loss has a direct influence on the propagation distance of the electromagnetic wave and on the signal transmission quality.
The electromagnetic wave suffers substantially no energy loss when propagating through a same medium. However, when the electromagnetic wave propagates through an interface between different media, partial reflection of the electromagnetic wave will occur. Usually, the larger the difference in electromagnetic parameters (e.g., the dielectric constant or the magnetic permeability) between the different media at two sides of the interface is, the more the reflection will be. Due to the partial reflection of the electromagnetic wave, the electromagnetic wave will suffer an electromagnetic energy loss in the propagation direction, which has a serious influence on the propagation distance of the electromagnetic wave and on the signal transmission quality.
To avoid reflection of the electromagnetic wave during propagation due to changes in refractive index and to reduce the reflection interferences and losses, usually impedance matching layers are disposed on a function dielectric sheet to reduce the reflection losses. Currently, the primary way to solve the problem of impedance matching during propagation of electromagnetic waves is to adopt an equal difference design, i.e., the refractive index distribution of the impedance matching layers satisfies the following formula:
            n      ⁡              (        i        )              =                  n                  m          ⁢                                          ⁢          i          ⁢                                          ⁢          n                    +                        i          ×                      (                                                            n                  g                                ⁡                                  (                  r                  )                                            -                              n                                  m                  ⁢                                                                          ⁢                  i                  ⁢                                                                          ⁢                  n                                                      )                                    i          +          1                      ,where i is No. of an impedance matching layer, ng (r) is a refractive index distribution function of the function dielectric sheet, and nmin is the minimum refractive index of the function dielectric sheet. Although the impedance matching layers satisfying the aforesaid formula can reduce the reflection interferences to some extent, the effect is not so significant. Therefore, an improved impedance matching technology is needed to reduce the reflection interferences and losses.
Further, in conventional optics, a lens can be used to refract a spherical wave radiated from a point light source located at a focus of the lens into a plane wave. Currently, the diverging effect of the lens is achieved by virtue of the refractive property of the spherical form of the lens. The inventor has found in the process of making this invention that, the lens has at least the following technical problems: the spherical lens is bulky and heavy, which is unfavorable for miniaturization; performances of the spherical lens rely heavily on the shape thereof, and directional propagation from the antenna can be achieved only when the lens has a precise shape; and serious interferences and losses are caused to the electromagnetic wave, which reduces the electromagnetic energy. Moreover, for most lenses, abrupt transitions of the refractive indices follow a simple line that is perpendicular to a lens surface. Consequently, electromagnetic waves propagating through the lenses suffer from considerable refraction, diffraction and reflection, which have a serious effect on the performances of the lenses.